1. Field of the Invention
The present invention relates to a method and apparatus for three dimensional image reconstruction. In particular, the present invention relates to a method and apparatus for reconstructing a three dimensional image of anatomical structures or regions of interest within a patient's body using stereotactic or isocentric backprojections.
2. Related Art
Three dimensional reconstruction of anatomical structures or regions of interest within a patient's body has always been important in many medical applications. Such information is used either alone or in conjunction with other clinical findings to reach a diagnosis or to formulate a treatment strategy. Many imaging devices and computer algorithms have been developed to provide such a capability with adaptations to the unique requirements of each clinical application. One example is Computed Tomography (CT) in which an X-ray source and detector assembly measure absorption profiles through a body from multiple directions. An algorithm based on the Fourier theorem is used in CT imaging to reconstruct the three dimensional anatomical structures as a sequence of two dimensional image slices.
Stereotactic radiography has long been established as the imaging modality for the precise localization and radiosurgical treatment of point targets within a patient's body. One example, in which stereotactic radiography is useful, is the application of stereotactic angiography in the diagnosis and treatment of arteriovenous malformations (AVM) in the brain. It has been noted that the present known angiography technique fails to provide a mechanism for accurate determination of the three dimensional shape or volume of the AVM. This deficiency leads to an overestimation of the size of the AVM, leading to radiation treatment of healthy brain tissue.
It has been suggested that if one can identify unique points of the AVM nidus on both the anterior-posterior (AP) and left-right (LATERAL) views of the AVM simultaneously, then the AVM can be reconstructed point by point in three dimensional space. Matching of such points of the nidus on both views, however, is almost impossible clinically. Significant research efforts have been dedicated to find an alternative approach for three dimensional visualization of the AVM. These efforts include contrast enhanced CT and Magnetic Resonance Angiography (MRA) for direct imaging of the AVM nidus.
CT angiography may often highlight the AVM, but it cannot clearly differentiate the feeding and draining vessels and the nidus containing the abnormal vascular shunts. It is critical to differentiate these components of the AVM for proper treatment. Early results from MRA are promising but there are several problems remaining in this process, such as geometric distortion associated with magnetic field inhomogeneities, gradient nonlinearities, susceptibility, chemical shift and flow shifts, that have not been fully addressed. Three dimensional visualization of vessel anatomy from MR datasets also remains restricted because of the inherent difficulty for automatic segmentation.
Conventional angiography, despite its limitations, provides temporal and spatial resolution of the AVM superior to that of CT and MR angiography. In fact, it is the only technique capable of resolving components of the AVM, such as the feeding artery, nidus and draining vein. The present invention is a new method which takes advantage of the precision of stereotactic angiography, and provides accurate three dimensional reconstruction of the AVM. Additionally, the present invention can be used in many other clinical applications to faithfully reconstruct an image of a region of interest within a patient's body.